Casting Method

ABSTRACT

[OBJECT] 
     To provide a method for casting with a gas permeable mold by gravity pouring, wherein melt is injected into only an intended cavity portion of a casting mold cavity and solidified. 
     [MEANS FOR ATTAINING THE OBJECT] 
     After pouring the melt having the volume substantially equal to that of the intended cavity portion to be filled with the melt, compressed gas is supplied from a sprue to inject the melt into the intended cavity portion and solidify the melt. The cavity may be decompressed before or after pouring according to need.

TECHNICAL FIELD OF THE INVENTION

This invention relates to an improvement in precision and productivity in a casting method in which gravity pouring of melt is carried out from the upper mold part or lateral part of a gas permeable mold.

BACKGROUND OF THE ART

A casting mold made from sand particles has been most commonly used as a gas permeable mold, and meanwhile, casting molds made from ceramic particles or metallic particles have been used extensively. A casting mold made of a material having even little air permeability such as calcium sulfate is deemed as the gas permeable mold, if it is mixed with a material having air permeability or made air permeability even in part. Where even an impervious metallic mold is provided with air holes or vent holes, it is also deemed as a type of gas permeable mold. Thus, the gas permeable mold according to the present invention includes these kinds of gas permeable molds.

A cavity in the casting mold is generally comprised of a sprue, a sprue runner, a riser and a product portion. There may be disposed an overflow for removing excessive melt from a product portion, but a structure basically comprising the sprue, sprue runner, riser and product portion will be described here for simplicity.

In all kinds of casting methods including as a general casting method and a peculiar casting method such as a vacuum casting method, pouring of the melt is completed upon filling of four cavity portions with the melt. After completing solidification of the melt, only the intended cast part molded in the product portion of these four portions is detached therefrom to taken out from the product portion, and then, the molded cast part is finished up to obtain a final cast product.

That is, the molded parts in the sprue, sprue runner and riser other than the product portion are separated as unnecessary cast parts from the intended cast part and subject to remelting as return materials. Although the unnecessary cast part formed in the riser is howbeit necessary for securing structural integrity of the product portion in a solidification process, the unnecessary cast parts in the sprue runner and sprue serve merely for filling the cavity with the melt.

Since volume expansion occurs due to crystallization of graphite in the solidification process in iron casting and so forth, it has been known that contraction quantity of the melt is partially compensated, so that a cast product having high integrity can be obtained under some conditions without using a riser. In this instance, the riser is also unnecessary, and it is only required to fill only the product portion with the melt.

As noted above, all the conventional casing methods adopt a pouring process for pouring melt into the unrequisite sprue, sprue runner and riser after all. Thus, this process is deemed very irrational. So, pouring yield represented as a ratio of the weight of product portion to the total pouring weight can be dramatically improved if only the product portion or the intended needful cavity portions such as the riser and product portion is filled with the melt in one way or another, consequently to solidify the melt in only the needful portions and, what is more, to enable significant simplification of the subsequent processes such as of mold dissection and product removal.

Although an investigation for prior art was conducted about a casting method in which gravity pouring of melt is carried out from the upper mold part or lateral part of a gas permeable mold, there could be found no prior art disclosing a casting method in which only the intended cavity portion of the casting mold cavities is filled with the melt.

As the casting method capable of filling only the intended cavity portion as described above, a vacuum casting method is deemed as the most potential casting method. Thus, the following Patent references 1 to 15 are enumerated as the prior art examples. However, all these patent references are concerned with a type of filling the melt into all the sprue, sprue runner, riser and product portion.

Patent Reference 1 (Japanese Published Unexamined Application SHO 61-180642A) discloses a vacuum casting method, which comprises disposing an air-permeable casting mold in a chamber and after closing a sprue with dissoluble material, and decompressing the chamber to a prescribed pressure to pour melt into the chamber.

Patent Reference 2 (Japanese Published Unexamined Application HEI 7-265998A) discloses a casting mold for vacuum casting, which has different mold thicknesses in a product cavity and gating cavity in a normal temperature curing type casting mold.

Patent Reference 3 (Japanese Published Unexamined Application No. 2003-170226A) discloses a vacuum casting method using a mold destined for entirely reducing the pressure, which incorporates a sensor so as to initiate a decompressing action in the mold after detecting pouring of melt into the mold by the sensor.

Patent Reference 4 (Japanese Published Unexamined Application HEI 3-216258A) discloses a decompression device in which the whole peripheral surface of a casting mold is airtightly covered with a sheet of resin film, and an exhaust port is disposed in a portion thoroughly distant from a sprue to reduce the pressure.

Patent Reference 5 (Japanese Published Unexamined Application SHO 60-124438A) discloses a vacuum casting method for performing pouring of melt after decompression in the suction box, in which a plaster casting mold formed by flaskless molding is placed on a suction box having ventholes and covered with a film sheet.

Patent Reference 6 (Japanese Published Examined Application HEI 7-115119B) discloses a vacuum casting method, in which a flask having upper and lower openings is provided within its lateral wall with a suction mechanism, and airtight sheets are attached to the upper and lower faces of the flask to perform aspiration for decompression in evaporative pattern casting.

Patent Reference 7 (Japanese Published Unexamined Application HEI 6-122060A) discloses a vacuum casting method for performing pouring under a decompressed state, in which a casting mold of organic caking additive is formed to a casting mold having ventholes and set within an open-topped chamber made of steel plate.

Patent Reference 8 (Japanese Published Unexamined Application HEI 8-10386A) discloses a vacuum casting method for performing pouring under a decompressed state, in which a sand mold is embedded in casting sand within an open-topped vacuum container.

Patent Reference 9 (Japanese Published Unexamined Application SHO 57-31463A) discloses a method for manufacturing a thin-thickness casting, in which the cavity is aspirated to pour melt thereinto through a venthole formed at the position most distant from a sprue of a mold.

Patent Reference 10 (Japanese Published Unexamined Application HEI 6-55255A) discloses a casting method for manufacturing a steel casting, in which casting is performed using a casting mold provided with a riser or an overflow at a position distant from an ingate, while decompressing by means of a hole formed in its vicinity in communication with the outside.

Also, the same Patent Reference 10 further discloses a method in which the pressure is reduced so as to make the rate of pouring melt constant by decompression-rate controlling means, and a method in which a mold level sensor is set in the ingate so as to start decompression immediately after detecting the melt.

Patent Reference 11 (Japanese Published Unexamined Application HEI 6-226423A) discloses a method for manufacturing a thin-thickness casting, in which an aspiration member having larger air permeability than a casting mold is disposed between a vacuum port and a riser or an overflow so as to make the degree of decompression in the cavity on the side of the vacuum port than that in the cavity on the side of sprue, similarly to the structure of the aforementioned Patent Reference 10.

Patent Reference 12 (Japanese Published Unexamined Application HEI 9-85421A) discloses a vacuum casting method in which decompression is performed through a hole communicating with the outside is formed in a core print set in a casting mold.

Patent Reference 13 (Japanese Published Unexamined Application HEI 9-85421A) discloses a casting mold for vacuum casting, which is provided with an aspirating guide for forming a passage between a portion to be decompressed in a internal space of a casting mold and the outside of the casting mold.

Patent Reference 14 (Japanese Published Unexamined Application SHO 60-56439A) discloses a plaster casting mold for vacuum casting, in which a filter of fire-resisting material having higher permeability compared with plaster is prepared from the vicinity of a final filling portion of the plaster casting mold to the outer surface thereof.

Patent Reference 15 (Japanese Published Examined Application HEI 7-41400B) discloses a vacuum casting method in which gas produced from a green sand mold and gas produced from a core are individually absorbed, and suction pressures are respectively adjustable freely.

To sum up the matter, all the conventional vacuum casting methods described in the foregoing patent references are featured in that the cavities in the casting mold are filled with melt. Therefore, the conventional vacuum casting methods are low in pouring yield, which is represented as a ratio of the weight of product portion to the total pouring weight, and make post-processes such as mold dissection and product removal cumbersome and complicated.

As stated above, none of the conventional art references describes or suggests a casting method capable of filling only an intended cavity in a casting mold with melt.

Patent Reference 1: Japanese Published Unexamined Application SHO 61-180642A

Patent Reference 2: Japanese Published Unexamined Application HEI 7-265998A

Patent Reference 3: Japanese Published Unexamined Application No. 2003-170226A

Patent Reference 4: Japanese Published Unexamined Application HEI 3-216258A

Patent Reference 5: Japanese Published Unexamined Application SHO 60-124438A

Patent Reference 6: Japanese Published Examined Application HEI 7-115119B

Patent Reference 7: Japanese Published Unexamined Application HEI 6-122060A

Patent Reference 8: Japanese Published Unexamined Application HEI 8-10386A

Patent Reference 9: Japanese Published Unexamined Application SHO 57-31463A

Patent Reference 10: Japanese Published Unexamined Application HEI 6-55255A

Patent Reference 11: Japanese Published Unexamined Application HEI 6-226423A

Patent Reference 12: Japanese Published Unexamined Application HEI 9-85421A

Patent Reference 13: Japanese Published Unexamined Application HEI 9-85421A

Patent Reference 14: Japanese Published Unexamined Application SHO 60-56439A

Patent Reference 15: Japanese Published Examined Application HEI 7-41400B

Non-patent Reference: None

DISCLOSURE OF INVENTION Problems To Be Solved By the Invention

In the light of the conventional art described above, the present invention was made to provide a casting method capable of filling only an intended cavity portion of mold cavities. According to the invention, the casting method can fulfill extremely high pouring yield and considerably simplify a post-process after mold dissection.

Means of Solving the Problems Means 1

A casting method for pouring melt having the weight volume ratio y into a gas permeable mold, characterized by filling an intended cavity portion with the melt with supply of a compressed gas from a sprue and solidifying the melt after initiation of pouring of the melt having the volume substantially equal to that of the cavity portion intended to be filled with the melt in a cavity of the gas permeable mold.

The cavities of the casting mold in the present means should be constructed to comprise a sprue, a sprue runner and a product portion for ease of explanation. And, an intended cavity portion to be filled with melt is the product portion.

First, the melt equal in volume to the product portion which is the intended cavity portion to be filled with the melt is poured into the product portion of the cavities of the gas permeable mold. The melt is poured into the mold through the sprue to partially fill the sprue runner and product portion with the melt. If remain untouched, the melt is dispersed into the respective cavities, so that the surfaces of the melts dispersed into the cavities become on the same level. Consequently, only the product portion of the intended cavity portion, which is designed to be filled with the melt in the present invention, cannot be filled with the melt.

With that in mind, in the first means according to the invention, a compressed gas is supplied from a sprue at an appropriate time after initiation of pouring of the melt to force the melt into the product portion with the pressure of the compressed gas, and then, the melt with which the product portion of the intended cavity portion is solidified. Since the melt is substantially equal in volume to the product portion of the intended cavity portion, only the product portion of the intended cavity portion can be filled with the melt.

In order to supply the melt having the volume substantially equal to that of the intended cavity portion, the melt may be measured in parts with respect to each casting mold by using a small ladle, or poured while being measured in one operation for one casting shot by using a large ladle. The substantially equal volume referred to here means the volume determined in view of suitable safety factor in consideration of uplift of an upper mold, which is caused in pouring the melt, and thermal expansion of the casting mold cavity.

As the compressed gas, a compressed air is generally easy-to-use and low cost. A compressed inactive nitrogen gas comes in useful in the sense of inhibiting oxidation of the melt.

When supplying the compressed gas, it is rather effective to prevent the compressed gas from leaking from the sprue by closing the sprue with a flange or the like of an air supply pipe in order to improve the operation of injecting the melt. Since leakage of the compressed gas from the outer periphery of the casting mold diminishes the operation of filling the intended cavity with the melt, it is desirable to take any measures to prevent the leakage of the compressed gas therefrom, if possible. Of course, it is not always necessary to take measures to prevent the leakage of the compressed gas when the casting mold is low in air permeability or covered entirely or partially with an airtight container or flask.

The appropriate time after initiation of pouring of the melt, at which the compressed gas is supplied from the sprue, is preferably determined as the earliest possible time during or after the course of passing of the aftermost melt through the sprue while pouring the melt. Because the filled melt begins to solidify when delaying the air supply, it is disadvantageously liable to develop defects such as cold shut and misrun or origination of oxide.

Solidifying of the filled melt does not necessarily imply that the melt filled into the casting mold solidifies entirely. Since outflow of the melt from a part of the intended cavity portion is caused from the vicinity of the boundary between the intended cavity portion filled with the melt and the other cavity portion, it is only necessary to solidify at least the melt stagnated around the boundary vicinity. Besides, there is no need to completely solidify the melt therearound, but the filled melt just has to be solidified so as to crystallize into a solid phase to the extend of preventing flowing of the filled melt out of the intended cavity portion. The details will be described below with reference to Embodiment 1.

Means 2

There is provided a casting method based on Means 1, which is characterized by supplying the compressed gas from the sprue to fill the intended cavity portion with the melt and solidifying the melt while maintaining the supply of the compressed gas.

This Means based on Means 1,in which the intended cavity portion is filled with the melt by using the compressed gas, resulting in solidifying the melt within the cavity portion, is featured in that the compressed gas is continuously supplied after filling the intended cavity portion with the melt to assure solidification of the melt. By continuing the supply of the compressed gas, it is possible to prevent the melt filled in the intended cavity portion with the supply of the compressed gas from flowing back from the vicinity of the boundary between the intended cavity portion and the other cavity portion and cause the melt in the boundary vicinity to solidify swiftly by the cooling action of the compressed gas. The details will be described below with reference to Embodiment 2.

Means 3

There is provided a casting method based on Means 1 or Means 2, which is characterized in that the applied pressure of the compressed gas is no less than the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion.

The casting method in which the product portion and riser are specified as the intended cavity portion to be filled with the melt in the case where the mold cavity comprises the sprue, sprue runner, riser and product portion, will be described. In order to prevent, more surely, the melt filled in the intended cavity portion from flowing out from the boundary vicinity toward the sprue runner, the applied pressure of the compressed gas should be defined to no less than the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion, where γ is the weight volume ratio (kgf/cm³) of the melt, H is the aforesaid height (cm), and thus, γH is the pressure (kgf/cm²).

The melt static pressure γH means a hydrodynamical melt static pressure under which the melt filled in the intended cavity portion is apt to flow out toward the sprue runner. Thus, it becomes possible to prevent the melt from flowing out by maintaining the applied pressure of the compressed gas thereabove.

The applied pressure of the compressed gas does not mean the pressure of the compressed gas and should be so designed that the pressure in the other cavity portion (cavity portions not yet filled with the melt) than the intended cavity portion becomes no less than the melt static pressure γH. The details will be described below with reference to Embodiment 3.

Means 4

There is provided a casting method based on Means 1 to 3, which is characterized in that the intended cavity portion is filled with the melt with supply of the compressed gas from the sprue, and there is used interrupting means for preventing the filled melt from flowing back from the vicinity of the boundary between the intended cavity portion and the other cavity portion.

The casting method makes use of the interrupting means for preventing the melt filled in the intended cavity portion from flowing back from the boundary vicinity. The details will be described below with reference to Embodiments 4 to 8.

Means 5

There is provided a casting method based on Means 4, which is characterized by using means for cooling the boundary vicinity as the interrupting means so as to prevent the melt filled therein from flowing back.

According to the casting method of this Means, solidification of the melt filled in the intended cavity portion can be accelerated to surely prevent the filled melt from flowing out toward the sprue runner by cooling the portion in the boundary vicinity. Although the applied pressure of the compressed gas is used for preventing the filled melt from flowing out, the casting method according to this Means can accelerate solidification of the melt filled in the intended cavity portion by flowing gas. Specifically, it is most effective to swiftly solidify the melt filled in the vicinity of the boundary between the intended cavity portion and the other cavity portion by the flow of gas. The compressed air is useful as the gas used here because it is significantly easy to use and low cost. Any safe gases can be used. Low-temperature gas is effective for expediting cooling. The details will be described below with reference to Embodiments 4 and 5.

Means 6

There is provided a casting method based on Means 4, which is characterized by using means for mechanically blocking the boundary vicinity as the interrupting means so as to prevent the melt filled therein from flowing back.

In the casting method of this Means, the boundary vicinity of the intended cavity portion filled with the melt and the other cavity portion are blocked. As the means for blocking the passage of the melt, a mold piece such as a shell mold having a shape coincident with the shape of the boundary vicinity may be pressed onto the boundary vicinity, or a blocking plate may be thrust into the mold in the boundary vicinity, by way of example. The details will be described below with reference to Embodiment 8.

Means 7

There is provided a casting method based on Means 1-6, which is characterized by decompressing the intended cavity portion to be filled with the melt before pouring the melt or after initiation of pouring of the melt.

In the casting method of this Means, in order to facilitating the filling of the melt into the intended cavity portion, the intended cavity portion to be filled with the melt is decompressed before pouring the melt or after initiation of pouring of the melt. By decompressed before pouring the melt, the poured melt can swiftly be introduced into the intended cavity portion, thereby to simplify control of timing of supplying the compressed gas and the pressure of the compressed gas after initiation of pouring of the melt. Besides, the decompression after initiation of pouring of the melt is not different in function and effect from that before pouring of the melt.

The difference between effects of decompression before pouring of the melt and after initiation of pouring of the melt is that the decompression before pouring of the melt can obtain a stable degree of decompression before filling the casting mold with the melt, but the degree of decompression changes with pouring the melt. The decompression after initiation of pouring of the melt brings about stable flow of the melt early in the course of pouring the melt because the initiation of pouring of the melt is commenced in a condition of atmosphere pressure, but a sufficient degree of decompression may not be obtained in the course of filling the cavity with the melt if the timing of commencing the decompression is delayed. The decompression before or after pouring of the melt, whichever is appropriate, may be applied in accordance with the quality of the melt and the shape of the mold cavity.

Although the whole casting mold may be decompressed, it is only necessary to decompress at least the intended cavity portion. The reduced pressure is maintained after filling the intended cavity portion with the melt. The details thereof will be described with reference to Embodiments 9 and 10.

Means 8

The casting method in either Means 1 or Means 6 is characterized in that, before pouring the melt or after initiation of pouring of the melt, the degree of decompression in the intended cavity portion to be filled with the melt is determined to a decompressed state of a pressure no less than the absolute value of the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion.

In this Means, the degree of decompression in the intended cavity portion to be filled with the melt before pouring the melt or after initiation of pouring of the melt is put into the decompressed state of a pressure no less than the absolute value of the melt static pressure γH. Hence, the intended cavity portion is filled with the melt up to the uppermost thereof even without supplying with compressed gas in pouring melt into the cavity, but the melt does not flow out from the boundary vicinity even after filing the cavity with the melt. Thus, the compressed gas supplied after initiation of pouring of the melt principally has a subsidiary effect of spill prevention by pressure and a cooling effect by gas current, thus to improve the collective stability in casting process. The decompression is maintained according to need even after filling the intended cavity with the melt The details will be described below with reference to Embodiment 9.

Means 9

There is provided a casting method based on Means 1-6, which is characterized in that the degree of decompression in the intended cavity portion to be filled with the melt is determined before pouring the melt or after initiation of pouring of the melt so as to bring the intended cavity portion into a decompressed state of a pressure less than the absolute value of the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion.

In this Means, the intended cavity portion is brought into a decompressed state in that the degree of decompression in the intended cavity portion is set to a pressure less than the absolute value of the melt static pressure γH. This is because inconvenience such as seizing of sand and turbulent flow of the melt may possibly be caused by the decompression, depending on the material of the melt and the shape of the casting mold cavity, when the degree of decompression is increased to not less than the absolute value of γH. In such a case, the degree of decompression should be made lower than the absolute value of γH (weak decompression) as proposed in this Means, so that the melt is gently introduced into the intended cavity portion and the seizing of sand is not caused by the complex effect of the decompression and pressurization of the compressed gas. The reduced pressure is maintained according to need after filling the intended cavity portion with the melt. The details thereof will be described with reference to Embodiment 10.

Effect of the Invention

The present invention achieves the following effects, which are beneficial compared with the conventional casting method.

To be more specific, in any conventional casting method, all parts of the mold cavity are filled with the melt, consequently to reduce the pouring yield represented as a ratio of the weight of product portion to the total pouring weight On the other hand, according to the present invention, only the necessary part of the cavity portion can be filled with the melt to be solidified, thus to dramatically improve the pouring yield. As a result, the melt required for forming a casting product can be spared considerably.

Since only the intended cavity portion is filled with the melt, only a molded part formed by solidifying the melt may be taken out from the cavity and processed upon mold dissection, consequently to considerably curtail the work operation in post-processing.

What it comes down to is that the following effects can be achieved by the present invention. (1) The considerable improvement in pouring yield enables reduction in melt usage, thus to reduce the energy and cost required for melting. (2) The work-hour in mold dissection can be remarkably reduced. These effects (1) and (2) make substantial contribution to CO₂ reduction, which is getting widespread international attention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention can be put into practice by any of the aforementioned Means 1 through Means 9, but as the best mode for carrying out the invention, there can be exemplified a casting method based on the aforementioned Means 7, in which the melt approximately equal in volume to the intended cavity portion in the state of decompressing the intended cavity portion to be filled with the melt before pouring the melt or after initiation of pouring of the melt. The degree of decompression and the pressure of the compressed gas are determined in consideration of the quality of the melt, the shape of the casting cavity and the casting method.

Although the present invention will be described with reference to the following embodiment, it is not to be considered limited to what is described in the specification.

EMBODIMENT 1

Embodiment 1 is illustrated in FIG. 1 and FIG. 2. In this embodiment carried out by the aforementioned Means 1, after initiation of pouring of the melt substantially equal in volume to the cavity portion intended to be filled with the melt in a cavity of the gas permeable mold, the intended cavity portion is filled with the melt while supplying a compressed gas from a sprue to solidify the melt.

First, the structure of a casting mold 1 will be explained. The casting mold 1 is a sand mold and formed of an upper mold flask 2 and a lower mold flask 3, which are placed on a mold stool 4 in the state of being superposed one on another to form a mold cavity therebetween. The mold cavity 7 includes a sprue 8, a sprue runner 9, and a product portion 11. In general, a riser is likely to be formed between the sprue runner 9 and product portion 11, but the casting mold in this embodiment has no riser.

In the casting method in this embodiment, which will be described here, the melt is introduced into only the product portion 11 as the intended cavity portion 12 within the mold cavity 7 and solidified therein. FIG. 1 illustrates the state in that the melt having the volume substantially equal to that of the cavity portion 12 intended to be filled with the melt is poured into the casting mold 1 by using a pouring ladle 13. As the melt 30 poured in the casting mold is approximately equal in volume to the product portion 11, the whole cavity cannot entirely be filled with the melt in such a manner that part of the melt is introduced into the product portion 11 and another part of the melt is stagnated in the sprue runner 9. Besides, there is seldom the melt head of the sprue 8, so that a force for inpouring the poured melt 30 into the product portion 11 is extremely small. As a result, if nothing is done, the product portion 11 cannot fully be filled with the poured melt 30 or long time is required, resulting in product failure.

With that in mind, as illustrated in FIG. 2, the compressed gas 16 made by a compression device 15 is supplied from the upper portion of the sprue 8, so that the melt 30 stagnated in the sprue runner 9 can be injected into the product portion 11 by the pressure of the compressed gas. In this embodiment, as the compressed gas, compressed air having pressure of 5 kgf/cm² and an air volume of 60 l/sec is used. There is attached a seal member 17 to a portion to which the compressed gas 16 is supplied in order to prevent gas leakage. Since the quantity of the poured melt is substantially equal to the volume of the product portion, only the product portion 11 as the intended cavity portion 12 comes eventually to be filled with the melt 30. Then, the poured melt 30 is solidified in this state.

The timing for supplying the compressed gas 16 does not always have to wait for the melt to stagnate in the sprue runner 9 as touched upon above. FIG. 1 illustrates the state in which the melt stagnates to account for the principle of the present invention, but does not show the preferred embodiment of the invention. Namely, the melt falls in temperature with increasing its stagnating time in the sprue runner, consequently to increase probability of causing defects such as cold shut, misrun and emergence of oxides. Therefore, it is advised to supply the compressed gas during or right after passage of the aftermost melt through the sprue 8 upon starting of pouring of the melt, so that the melt can be smoothly injected into the intended cavity portion 12 without causing stagnation of the melt in the sprue runner 9. This is a practical use for the embodiment. As to the timing for supplying the compressed gas, the same holds for the following embodiments.

In the manner described above, the melt could be injected into only the product portion which is a part of the intended cavity portion within the mold cavity, thus to be solidified. Since the product portion in this embodiment is formed in the lower mold part of the casting mold, it may be as well to halt supply of the compressed gas supply or slightly supply the compressed gas to expedite solidification of the melt.

The term “solidification” is broadly interpreted as a phenomenon of solidifying the melt in the whole product portion, which is the intended cavity portion in the mold cavity, but narrowly means that the melt is solidified in the vicinity of the boundary between the intended cavity portion and the other cavity portion without allowing the filled melt to flow out toward the sprue runner 9. To be specific, the narrowly-defined solidification means that the melt in the boundary vicinity is solidified until losing fluidity due to solid phase crystallization of the melt. That is, the present invention aims at introducing the melt into only the intended cavity portion and solidifying the melt there, but it is only necessary to carry on the injection and solidification of the melt in various manners until the melt solidifies in the narrow sense of the meaning. The same is true on the following embodiments.

When the compressed gas is supplied, the gas partially escapes through between the particles forming the casting mold having gas permeability, thus to reduce the activity of injecting the melt into the cavity. With this point in view, the pressure and gas volume of the compressed gas may be adequately regulated to ensure a sufficient action of injecting the melt. Alternatively, it is effective to seal the casting mold with impervious material according to need.

In general, a compressed air as the compressed gas is most easy-to-use and low cost. Instead, inert gases such as compressed nitrogen can effectively be used. The pressure and gas volume of the compressed gas are determined in consideration of gas permeability of the casting mold, the shape of the mold flask, the overall sealing degree of the mold, casting design and so on.

In the conventional casting method, the melt is poured into the entire cavity in the casting mold. However, the casting method according to the present invention makes it possible to inject the melt into only the intended cavity portion, so that the injected melt is solidified in the intended cavity portion. As a result, pouring yield represented as a ratio of the weight of product portion to the total pouring weight can be dramatically improved. As an example, the pouring yield, which was about 50% to 70% at the most according to the conventional casting method, can be improved to about 100%, consequently to save on the melt significantly.

According to this embodiment of the invention, the melt is fed into only the product portion in the cavity, but does not exist in the sprue 8 and sprue runner 9. Thus, all that is left is a simple operation of taking out a resultant molded part formed by solidifying the melt injected into only the product portion, consequently to substantially lighten the work load.

EMBODIMENT 2

Embodiment 2 is illustrated in FIG. 3 and FIG. 4. In this embodiment carried out by the aforementioned Means 2, the melt is injected into the intended cavity portion by supplying the compressed gas after initiation of pouring of the melt and solidified with maintenance of supplying the compressed gas.

FIG. 3 illustrates the state after the melt 30 is poured into the product portion 11 as the intended cavity portion 12. The structure formed of the casting mold 1 and mold cavity 7 is identical to that in Embodiment 1 except that a cover member 18 made of iron is disposed on the upper mold flask 2 to secure airtightness. The cover member 18 is provided to enhance the efficiency of the pressure of the compressed gas. It is desirable to make the cover member 18 of impervious material, but the equivalent effect can be achieved even by using the cover member made of a material lower in gas permeability than the casting mold.

In the state after pouring the melt as illustrated in FIG. 3, the volume of the poured melt is substantially equal to that of the product portion 11 similarly to Embodiment 1, besides, there is seldom the melt head of the sprue 8, thus a part of the melt 30 is introduced into the product portion 11 and another part of the melt to stagnate in the sprue runner 9.

Next, as the compressed gas 16 made by the compression device 15 is supplied from the upper portion of the sprue 8 as shown in FIG. 4, the melt 30 in the sprue runner 6 is injected into the product portion 11 by the action of the compressed gas 16 similarly to Embodiment 1. The upper portion of the upper mold flask 2 is covered with the cover member 18 to secure airtightness in this embodiment, consequently to diminish leakage of the compressed gas 16 from the casting mold 1. Consequently, the compressed gas serves to make an action to inject the melt into the product portion 11 with higher efficiency than in Embodiment 1. In this embodiment, as the compressed gas, compressed air having pressure of 5 kgf/cm² and an air volume of 60 l/sec was used.

The supplying of the compressed gas 16 is retained to impart moderate pressure after injecting the melt 30 into the product portion 11, so that the injected melt 30 can be solidified without causing the melt to flow out from the product portion 11. The pressure and gas volume of the compressed gas 16 are adequately determined in accordance with the type of the casting mold, the casting design and so forth.

This embodiment makes it possible to inject the melt into the intended cavity portion and solidify the injected melt more stably than Embodiment 1.

As stated in Embodiment 1, the timing for supplying the compressed gas does not always have to wait for the melt to stagnate in the sprue runner. It is a practical embodiment that the compressed gas is supplied swiftly during or after the course of passing of the aftermost melt through the sprue to smoothly inject the melt into the intended cavity portion without causing stagnation of the melt in the sprue runner.

EMBODIMENT 3

Embodiment 3 is illustrated in FIG. 5 and FIG. 6. In this embodiment carried out by the aforementioned Means 3, a part of the intended cavity portion having a certain height, which is formed in the upper mold part, is filled with the melt by supplying specifically-defined pressure of the compressed gas to be solidified there.

As shown in FIG. 5, the casting mold 1 has the substantially same in structure as that in Embodiment 2, and the mold cavity 7 comprises the sprue 8, sprue runner 9, riser 10 and product portion 11. The product portion 11 is formed within an upper mold 5 and a lower mold 6, and the part of the product portion 11 in the upper mold has a height H. In this embodiment, the intended cavity portion 12 formed of the product portion 11 and riser 10 is filled with the melt to be solidified there. The aforementioned height H is equivalent to a height from a cavity inlet from which the melt inflows into the intended cavity portion.

FIG. 5 shows the state after pouring the melt 30 substantially equal in volume to the intended cavity portion 12. Similarly to Embodiments 1 and 2, the volume of the melt poured is substantially equal to that of the intended cavity portion, and besides, there is seldom the melt head of the sprue 8. That is, the melt 30 is partially filled in the whole cavity, falling on horizontal level.

As shown in FIG. 6, the melt 30 is injected into the intended cavity portion 12 while supplying the compressed gas 16 from the upper portion of the sprue 8 similarly to Embodiments 1 and 2, and then, the melt 30 is solidified while supplying the compressed gas 16. In this embodiment, the applied pressure of the compressed gas 16 is determined to not less than γH where y is a weight volume ratio (kgf/cm³) of the melt, and H is a height (cm) from a cavity inlet from which the melt inflows into the intended cavity portion to the uppermost part of the intended cavity portion 12. Hence, γH is a pressure (kgf/cm²). For instance, when cast-iron melt having a weight volume ratio of γ=7×10⁻³ kgf/cm³ is injected into a casting mold cavity of H=20 cm, the equation “γH=0.14 kgf/cm²” is satisfied.

The value γH has a meaning of a melt static pressure by which the melt 30 filled in the intended cavity portion 12 attempts to flow out from the boundary vicinity 19 between the intended cavity portion 12 and the other cavity portion 20 toward the sprue runner 9. Therefore, the melt 30 can be injected into the intended cavity portion 12 up to the uppermost of the intended cavity portion by the action of the applied pressure not less than γH of the compressed gas 16. By maintaining the applied pressure of the compressed gas, the melt 30 filled in the cavity portion can be stopped flowing out. Incidentally, the applied pressure not less than γH does not mean the pressure of the compressed gas, but has a meaning that the pressure in the boundary vicinity 19 is kept not less than γH in consideration of leakage of the compressed gas 16 from the casting mold 1.

As shown in this embodiment, even when the intended cavity portion 12 to be filled with the melt is placed high above the cavity inlet of the melt, the melt 30 is injected into the intended cavity portion 12 by supplying the compressed gas 16, which has the applied pressure of not less than the melt static pressure γH determined by the weight volume ratio γ of the melt and the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion, and maintaining the applied pressure of the compressed gas, so that a desired casting product can be obtained from the melt injected into only the product portion 11 and the riser 10 of the intended cavity portion 12.

As stated in Embodiments 1 and 2, the timing for supplying the compressed gas does not always have to wait for the melt to stagnate in the sprue runner as shown in FIG. 5. It is a practical embodiment that the compressed gas is supplied swiftly during or after the course of passing of the aftermost melt through the sprue to smoothly inject the melt into the intended cavity portion without causing stagnation of the melt in the sprue runner.

EMBODIMENT 4

Embodiment 4 is illustrated in FIG. 7. In this embodiment carried out by the aforementioned Means 4 and Means 5, the melt is injected into the intended cavity portion by supplying the compressed gas from the sprue after initiation of pouring of the melt and cooling the vicinity of the boundary between the intended cavity portion and the other cavity portion to solidify the melt.

FIG. 7 illustrates the state of supplying the compressed gas 16 from the upper part of the sprue 8 after pouring the melt having the volume substantially equal to that of the intended cavity portion 12. With supply of the compressed gas 16, the melt 30 is injected into the product portion 11 and the riser 10 of the intended cavity portion 12. The structure formed of the casting mold 1 is approximately equal to that in Embodiment 3 except that a venting hole 21 formed in the upper part of the boundary vicinity 19 between the intended cavity portion 12 and the other cavity portion 20.

The function of this embodiment will be explained on the basis of this structure. The melt 30 is injected into the intended cavity portion 12 with supply of the compressed gas 16 after initiation of pouring of the melt, and then, by continuing the supply of the compressed gas 16, the compressed gas flows through the venting hole 21 for allowing the gas to pass through most easily, while conducting heat away from the boundary vicinity 19 to cool the boundary vicinity. Consequently, the boundary vicinity 19 is rapidly cooled to solidify the melt, thus to shorten the amount of time required for supplying the compressed gas 16. That is, the compressed gas 16 is used for having an effect for injecting the melt 30 and a cooling effect.

Meanwhile, if the venting hole 21 is not formed, the compressed gas 16 is allowed to escape through between the particles forming the casting mold by maintaining the applied pressure of the compressed gas, and therefore, the boundary vicinity 19 is cooled at a certain speed. However, this embodiment has higher cooling capacity to solidify the melt promptly.

As stated above, the time to maintain the supply of the compressed gas after injecting the melt into the intended cavity portion can be shortened by providing the venting hole for cooling the boundary vicinity with the compressed gas, thus to solidify the melt promptly. Consequently, the production efficiency can be enhanced when applying the present invention to an actual production line.

EMBODIMENT 5

Embodiment 5 is illustrated in FIG. 8. In this embodiment carried out by the Means 4 and Means 5 similarly to Embodiment 4 as above, the melt is injected into the intended cavity portion by supplying the compressed gas from the sprue after initiation of pouring of the melt and cooling the vicinity of the boundary between the intended cavity portion and the other cavity portion with the compressed gas to solidify the melt.

FIG. 8 illustrates the state of supplying the compressed gas 16 from the upper part of the sprue 8 after pouring the melt 30 having the volume substantially equal to that of the intended cavity portion 12. With supply of the compressed gas 16, the melt 30 is injected into the product portion 11 and the riser 10 of the intended cavity portion 12. The structure formed of the casting mold 1 is approximately equal to that in Embodiment 4 except that a venting hole 21 formed in the upper part of the boundary vicinity 19 between the intended cavity portion 12 and the other cavity portion 20. In this embodiment, a gas supply pipe 22 is disposed separately from the sprue 8, so that the compressed gas 16 can be supplied from the upper part of the venting hole 21. The gas supply pipe 22 is provided with a valve 23.

The function of this embodiment will be explained on the basis of this structure. After injecting the melt 30 from the sprue 8 into the intended cavity portion 12 with the compressed gas 16, the valve 23 of the gas supply pipe 22 disposed above the venting hole 21 is open to supply the compressed gas 16 to the venting hole 21, thus to cool the boundary vicinity 19 rapidly with both the supply of gas from the sprue 8 and the supply of gas from the venting hole 21. As a result, similarly to Embodiment 4, the amount of time required for supplying the compressed gas 16 can be shortened after filling the intended cavity portion 12 with the melt 30, so that the production efficiency can be enhanced when applying the present invention to an actual production line.

EMBODIMENT 6

Embodiment 6 is illustrated in FIG. 9 and FIG. 10. In this embodiment carried out by the aforementioned Means 4 and Means 6, the intended cavity portion is filled with the melt while supplying a compressed gas from a sprue, and the vicinity of the boundary between the intended cavity portion and the other cavity portion is mechanically blocked.

FIG. 9 illustrates the state in that the melt 30 having the volume substantially equal to that of the intended cavity portion 12 is poured into the mold cavity. In this embodiment, as shown in FIG. 10, after pouring the melt, a mold piece 24 made of a shell mold is put into the sprue 8, and then, the melt 30 is injected into the intended cavity portion 12 with supplying the compressed gas 16 from the sprue 8, while thrusting the mold piece 24 into the boundary vicinity 19. The boundary vicinity 19 conforms in shape to the mold piece 24, thereby to prevent flowing out of the melt 30. The part of melt 30 in contact with the mold piece 24 is solidified rapidly, so that the time to maintain the compressed gas 16 can be shortened. Although the mold piece 24 formed of a sand mold such as a shell mold is easy-to-use and low cost, the mold piece made of fire-resistant material being smaller in specific gravity than the melt can achieve the same effect and function.

According to this embodiment, the melt can be solidified swiftly by obstructing the passage of the filled melt, so that the production efficiency can be enhanced when applying the present invention to an actual production line.

EMBODIMENT 7

Embodiment 7 is illustrated in FIG. 11 and FIG. 12. In this embodiment carried out by the aforementioned Means 4 and Means 6, the intended cavity portion is filled with the melt while supplying a compressed gas from a sprue, and the vicinity of the boundary between the intended cavity portion and the other cavity portion is mechanically blocked.

FIG. 11 illustrates the state immediately before the melt 14 having the volume substantially equal to that of the intended cavity portion 12 is poured into the mold cavity. In this embodiment, there is formed a concave portion 25 in the lower mold in the boundary vicinity 19 of the mold cavity 7 so as to mount a blocking piece 26 of a shell mold therein.

FIG. 12 shows the state in which the melt 30 is injected into the intended cavity portion 12 with supply of the compressed gas 16 after initiation of pouring of the melt. When the melt 30 is filled in the cavity portion, the blocking piece 26 mounted in the concave portion 25 floats with its buoyancy and comes in contact with the upper wall of the sprue runner, consequently to obstruct the passage of the melt 30. Thus, the blocking piece 26 serves to prevent flowing out of the melt 30 and expedite cooling of the melt in the boundary vicinity 19 as a result of coming in contact with the melt 30. Hence, since the time to supply the compressed gas 16 can be shortened, the production efficiency can be enhanced when applying the present invention to an actual production line.

EMBODIMENT 8

Embodiment 8 is illustrated in FIG. 13. In this embodiment carried out by the aforementioned Means 4 and Means 6, the intended cavity portion is filled with the melt while supplying a compressed gas from a sprue, and the vicinity of the boundary between the intended cavity portion and the other cavity portion is mechanically blocked.

FIG. 13 shows the state in which the melt 30 is injected into the intended cavity portion 12 with supply of the compressed gas 16 after initiation of pouring of the melt 30 substantially equal in volume to the intended cavity portion 12. In this embodiment, a venting hole 21 is formed in the upper part of the boundary vicinity 19, so that a blocking plate 27 is plunged into the casting mold in the boundary vicinity 19 through the venting hole 21, thus to block the melt 30. In this case, the venting hole 21 conforms in shape to the blocking plate 27.

This embodiment makes it possible to prevent flowing out of the melt 30 by directly plunging the blocking plate 27 into the boundary vicinity 19 after injecting the melt 30, so that the need for waiting for solidification of the melt can be eliminated, and therefore, the supply of the compressed gas 16 can be ceased immediately after blocking. Consequently, the production efficiency can be enhanced when applying the present invention to an actual production line.

The method for blocking in the boundary vicinity of Means 6 is illustrated in Embodiment 6 through 8 by way of example, but, in short, what that means is that the filled melt is prevented from flowing out by using some suitable kind of blocking means. Any other means can achieve the same effect and function.

EMBODIMENT 9

Embodiment 9 is illustrated in FIG. 14 through FIG. 16. In this embodiment carried out by the aforementioned Means 7 and Means 8, the intended cavity portion is decompressed to promptly fill the intended cavity portion with the poured melt before pouring the melt or after initiation of pouring of the melt, and according to need, after pouring the melt, the intended cavity portion is further decompressed while supplying the compressed gas from the sprue.

FIG. 14 illustrates the state immediately before the melt 14 having the volume substantially equal to that of the intended cavity portion 12 is poured into the mold cavity. In the casting mold 1, the venting hole 21 is formed respectively at the upper part of the cavity of the product portion 11 and the riser 10 of the intended cavity portion 12. On the upper mold flask 2, there is disposed a decompression hood 29 in communication with a decompression device 28. The venting hole 21 has a decompression action strongly on the intended cavity portion 12, so that a desired degree of decompression can be stably maintained. However, the venting hole is not necessarily indispensable in the present invention, but it is only necessary to put the intended cavity portion to a prescribed degree of decompression.

The degree of decompression of the intended cavity portion 12 is increased to not less than the absolute value of γH by decreasing the pressure from the upper mold 5. In γH, γ is the weight volume ratio of the melt, and H is the height from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion. The height H is equivalent to the height of the upper mold portion of the product portion 11 in this embodiment. γH is the melt static pressure by which the melt 30 filled in the intended cavity portion 12 attempts to flow out from the boundary vicinity.

FIG. 15 illustrates the state after pouring the melt. The poured melt 30 is smoothly injected to the uppermost of the intended cavity portion 12, since the intended cavity portion 12 is decompressed to not less than γH. As the sprue 8 is open to the air after initiation of pouring the melt, the degree of decompression changes. Thus, as shown in FIG. 16, it is possible to prevent flowing out of the poured melt, which is injected from the upper part of the sprue 8 with supply of the compressed gas 16, and rapidly cool the melt in the boundary vicinity 19 by the cooling action of the compressed gas 16 to be solidified rapidly.

The decompression caused by the decompression device is continuously maintained until solidifying the melt filled in the intended cavity portion according to need. That is, the inside of the intended cavity portion is decompressed before pouring the melt or after initiation of pouring of the melt so as to smoothly inject the melt into the intended cavity portion, and then, the heat of the casting mold is effectively dissipated to rapidly solidify the melt with maintaining the decompression in the intended cavity portion, while preventing the poured melt from flowing out of the boundary vicinity by the compressed gas.

The timing of commencing the decompression may be the time before pouring the melt as performed in this embodiment or after initiation of pouring of the melt. Both the timing can achieve the same function and effect. However, there is a difference in change of the degree of decompression in the casting mold cavity between the timing before pouring the melt and the timing after initiation of pouring of the melt. To be specific, the decompression before pouring the melt enables the casting mold cavity to be maintained at a stable degree of decompression before pouring the melt, but the degree of decompression in the casting mold cavity changes as the melt is poured. The decompression after initiation of pouring of the melt enables the stability of the flowing of the melt in the early phase of pouring of the melt because the pouring is carried out in atmospheric pressure, but there are cases where a ample degree of decompression may not be assured in the process of pouring the melt when the timing of commencing the decompression is delayed. The decompression before or after pouring of the melt, whichever is appropriate, may be applied in accordance with the quality of the melt and the shape of the mold cavity.

As is described above, by combining the decompression and the supply of the compressed gas, the injection of the melt into the intended cavity portion can be more stably carried out, thus to promptly solidify the melt.

EMBODIMENT 10

Embodiment 10 is illustrated in FIG. 17 and FIG. 18. In this embodiment carried out by the aforementioned Means 7 and Means 9, the intended cavity portion is decompressed at a low degree of decompression (weak decompression) to promptly fill the intended cavity portion with the poured melt before pouring the melt or after initiation of pouring of the melt, and according to need, after pouring the melt, the intended cavity portion is further decompressed while supplying the compressed gas from the sprue.

FIG. 17 illustrates the state immediately before the melt 14 having the volume substantially equal to that of the intended cavity portion 12 is poured into the mold cavity. In the embodiment, the casting mold has no venting hole. The intended cavity portion 12 in this embodiment is decompressed to a pressure less than the absolute value of the melt static pressure γH (weak compression) before pouring the melt The poured melt 30 can be smoothly introduced into the intended cavity portion 12 thus decompressed. However, as the degree of decompression is lower than the absolute value of γH, the melt 30 cannot be introduced up to the uppermost of the intended cavity portion 12.

Therefore, as shown in FIG. 18, the melt 30 is introduced up to the uppermost of the intended cavity portion 12 by supplying the compressed gas 16 from the upper part of the sprue 8. Thereafter, solidification of the melt in the boundary vicinity 19 is expedited in this state. The decompression may be maintained according to need. To expedite solidification of the melt in the shortest possible time, it is preferable to maintain or strengthen the decompression. The timing of commencing the decompression may be the time before pouring the melt as performed in this embodiment or after initiation of pouring of the melt.

The reason why the degree of decompression is less than the absolute value of γH in this embodiment is because inconvenience such as turbulent flow of the melt and emergence of the oxidization of the melt may possibly be caused by the decompression, depending on the material of the melt and the shape of the casting mold cavity. In such a case, there had better introduce the melt into the intended cavity portion at a rather low degree of decompression as in this embodiment, filling the melt into the intended cavity portion in tandem with the supplying action of the compressed gas and solidifying the melt.

FIG. 19 illustrates the state of pouring the melt when the intended cavity portion to be filled with the melt includes the product portion, riser and sprue runner. The processes of pouring the melt and decompressing and pressurizing the intended cavity portion are the same as described above. The pouring yield in this case is decreased as the quantity of the poured melt is increased, but this embodiment is superior in that the melt can be injected infallibly into the critical portions in casting such as the product portion or the combined product portion and riser, without concern for weighing accuracy of the quantity of the melt to be poured. Since the casting mold has no sprue, the pouring yield can be improved by about 10% to 15% in the case of such a quantity of the poured melt.

In casting a plurality of castings with a single casting mold having the intended cavity portions comprising only the product portions and risers as shown in FIGS. 17 and 18, it is necessary to dispense the pouring melt respectively to the plural product portions and risers as uniform as possible. On the contrary, the casting mold having the intended cavity portions comprising the product portions, risers and sprue runners as shown in FIG. 19 is superior in that the pouring melt can be injected into the intended cavity portions without taking into consideration of the need for uniformly dispensing the pouring melt into the intended cavity portions.

Thus, the intended cavity portion to be filled with the melt may be adequately designed depending on the situation. For instance, the product portion, riser and a part of sprue runner may be formed in the intended cavity portion. Further, in the case of the casting mold having no riser, the product portion and a part of sprue runner may be formed in the intended cavity portion. The same applies validly to all Embodiments 1 to 10.

Embodiments 9 and 10 in which decompression and supply of compressed gas are effected in combination enables more stable injection and solidification of the melt relative to the intended cavity portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing the state after pouring melt in Embodiment 1 of the present Invention.

FIG. 2 is a view showing supply of compressed gas in Embodiment 1 of the present invention.

FIG. 3 is a view showing the state after pouring the melt in Embodiment 2 of the present invention.

FIG. 4 is a view showing the supply of compressed gas in Embodiment 2 of the present invention.

FIG. 5 is a view showing the state after pouring the melt in Embodiment 3 of the present invention.

FIG. 6 is a view showing the supply of compressed gas in Embodiment 3 of the present invention.

FIG. 7 is a view showing Embodiment 4 of the present invention.

FIG. 8 is a view showing Embodiment 5 of the present invention.

FIG. 9 is a view showing the state after pouring the melt in Embodiment 6 of the present invention.

FIG. 10 is a view showing the supply of compressed gas in Embodiment 6 of the present invention.

FIG. 11 is a view showing the state before pouring the melt in Embodiment 7 of the present invention.

FIG. 12 is a view showing the state after pouring the melt in Embodiment 7 of the present invention.

FIG. 13 is a view showing Embodiment 8 of the present invention.

FIG. 14 is a view showing the state before pouring the melt in Embodiment 9 of the present invention.

FIG. 15 is a view showing the state after pouring the melt in Embodiment 9 of the present invention.

FIG. 16 is a view showing the supply of compressed gas in Embodiment 9 of the present invention.

FIG. 17 is a view showing the state before pouring the melt in Embodiment 10 of the present invention.

FIG. 18 is a view showing the state after pouring the melt in Embodiment 10 of the present invention.

FIG. 19 is another view showing the state after pouring the melt in Embodiment 10 of the present invention.

EXPLANATION OF REFERENCE NUMERALS

1 Casting mold

2 Upper mold flask

3 Lower mold flask

4 Mold stool

5 Upper mold

6 Lower mold

7 Mold cavity

8 Sprue

9 Sprue runner

10 Riser

11 Product portion

12 Intended cavity portion

13 Pouring ladle

14 Melt

15 Compression device

16 Compressed gas

17 Seal member

18 Cover member

19 Boundary vicinity

20 Other cavity portion

21 Venting hole

22 Gas supply pipe

23 Valve

24 Mold piece

25 Concave portion

26 Blocking piece

27 Blocking plate

28 Decompression device

29 Decompression hood

30 Poured melt

31 Packing member

32 Resin foam plate 

1. A casting method for pouring melt having the weight volume ratio γ into a gas permeable mold, characterized by filling an intended cavity portion with the melt with supply of a compressed gas from a sprue and solidifying the melt after initiation of pouring of the melt having the volume substantially equal to that of the cavity portion intended to be filled with the melt in a cavity of said gas permeable mold.
 2. The casting method set forth in claim 1, characterized by supplying the compressed gas from the sprue to fill the intended cavity portion with the melt and solidifying the melt while maintaining the supply of said compressed gas.
 3. The casting method set forth in claim 1, wherein the applied pressure of the compressed gas is no less than the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of said intended cavity portion.
 4. The casting method set forth in claim 1, wherein by filling the intended cavity portion with the melt with supply of the compressed gas from the sprue and using interrupting means so as to prevent the melt filled therein from flowing back from the vicinity of the boundary between said intended cavity portion and the other cavity portion.
 5. The casting method set forth in claim 4, further characterized by using means for cooling the vicinity of the boundary as the interrupting means so as to prevent the melt filled therein from flowing back.
 6. The casting method set forth in claim 4, further characterized by using means for mechanically blocking the vicinity of the boundary as the interrupting means so as to prevent the melt filled therein from flowing back.
 7. The casting method set forth in claim 1, wherein by decompressing the intended cavity portion to be filled with said melt before pouring the melt or after initiation of pouring of the melt.
 8. The casting method set forth in claim 1 wherein the degree of decompression in the intended cavity portion to be filled with said melt is determined before pouring the melt or after initiation of pouring of the melt so as to bring the intended cavity portion into a decompressed state of a pressure no less than the absolute value of the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of said intended cavity portion.
 9. The casting method set forth in claim 1, wherein the degree of decompression in the intended cavity portion to be filled with said melt is determined before pouring the melt or after initiation of pouring of the melt so as to bring the intended cavity portion into a decompressed state of a pressure less than the absolute value of the melt static pressure γH determined by the height H from a cavity inlet for introducing the melt into the intended cavity portion to the uppermost of the intended cavity portion. 